Electromagnetic-wave-receiving system



O. C. ROOS July 14, 1925, 1,545,697

ELECTROMAGNETIC WAVE RECEIVING SYSTEM Original FiledNov. 4, 1921 9 Sheets-Sheet 1 T *4! r I July 14, 1925.

0. C. ROOS BLBGTROIMQNBTIC WAVE RECEIVING SYSTEM Orizinal Filed Nov. 4. 1921 9 Sheets-Sheet 5 6 7t Inf 00 Jul 14, 1925.

O. C. ROOS ELECTROMAGNETIC WAVE RECEIVING SYSTEM Original Filed Nov. 4, 1921 9 Sheets-Sheet 4 Zkvezzi'a 0% a Q:

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' July 14,1925.

ELECTROMAGNETIC WAVE RECEIVING SYSTEM 9 Sheets-Sheet 5 Original Filed Nov. 4, 1921 July 14, '1925.

0. c. Roos ELECTROHAGNETIC WAVE RECEIVING SYSTEM 9 Sheets-Sheet 6 AVA 0. C. RODS ELECTROMAGNETIC WAVE RECEIVING SYSTEM July 14, 1925 Original Filed Nov. 4, 1921 9 Sheets-Sheet 7 July 14, 1925; 1,545,697

0. C. ROOS ELECTROMAGNETIC WAVE RECEIVING SYSTEM Original Filed Nov. 4, 1921 9 Sheets-Shet a July 14, 1925.

O. C. R005 ELECTROMAGNETIC WAVE RECEIVING SYSTEM Original FiledNov'. 4, 1921 9 Sheets-Sheet 9 ,zzwflza Mack Patented July 14, 1925.

' UNITED STATES PATENT"oF-FicEa OSCAR c. noos, or BOSTON, MASSACHUSETTS.

ELECTROMAGNFETIG VJAVE-RECEIViNG SYSTEM. 1

,, Application filed November 4, 1921. Serial No. 512,785.

To all whom it may concern:

Be it known that 1, Oscar: C. Boos, a citi- I zen of the United States, and a resident of Boston, in the county of Suffolk and State or Massachusetts, have invented ,a new and useful Improvement in Electromagnetic-- ave-Receiving Systems, of which thebfollowing is a specificat on;

sipgnal-indicating device of electrical vibrations created in the system by abrupt or 1m:

pulsive electrical forces, such for example,

as static disturbances, so called, or electrical vibrations created in the system by interfering signal Waves, is eliminated or reduced to a minimum so that the signal-interference ratio is a maximum.

My invention based on my discovery that the irregular nonmusical noises or nonharmonic vibrations produced by a; signalindicat ng device such as telephone receiver when the receiving system is acted upon byabrupt or impulsive electrical forces i may be converted into spatialized periodic vibrations. ,1

In carry ng out my invention I provide means for converting the electrical vibra tions developedlin the receiving system by ,abrupt orimpulsive electrical torees and,

the electrical vibrations developed therein by the electromagnetic Wavesthe energy of which is to be received into dephased spatialiaed non-electrical vibrations, such fore); ample as sonorous vibrations"produced in an air column, an apparatus so associated with said means that the amplitude therein oi? the non-electrical vibrations resulting from the Waves the energy of Which is to be received islarge compared to the amplitude therein of the non-electrical vibrations resulting from the abrupt orimpulsive electrical forces, and a signal-indicating device associated with said apparatus. The non-; electrical vibrations WhlCll pass ito said apparatus may be converted into electrical vibrations by any suitable means, and in suchcase a signal-indicating device isopcrativelyconnectedvith said means v My invention comprises ineansffor ccnverting the irregular complex noisesproducedby a signal-indicating device, such as a telephone receiver, when the receiving system is acted upon by abrupt or impulsive v et e Q QQ y n eowel de r's 1 study the air chamber Will produce a resultant v sound-Wave produced acoustic vibrations of any convenient pitch, such means consisting, for example, of resonant air chamber so designed that when theconfined body of air therein is shocked into vibration at its own period, an acoustic vibration different in pitch from that of the signal Wlll l'JQ- produced, the pitch of which signal is under complete control of the op: erator by means of the heterodyne. L The' complex sound, consisting of the acoustic vibrationproduced by the signal avesandy the non-musical noise produced by,.tliekelee, trical disturbance, Which is introduced into,

7O complex vibration which thesuniof its components, but which when of audible. pitch is different in sound from either, My invention comprises also a mean-stoic spatializing the two sound Waves making up; the resultant acoustic yibration aforesaid, such means being, for example a resonant, air-chamber of such dimensions that the tivo sets of vibrations Willproducestationary; sound-waves therein which, being oi d'ifler- 8O ent frequencies, Will be depliased. Means are provided for picking upthe stationa by the sigiiaflfiva'ves' at a point, here the amplitude thereof is large compared to, the amplitude of the stationary sound-Wave formed the electrical di.sturbance, for example, at a pressure loop of the former and apress'ure node of the latter.

Having separated the two sets of sound.

Waves and picked up a portion of the energy 'waves into electrical vibrations, and trans? Hill; the latter to a signal-indicating device.

By transmission through several stationary- Wave separating devices in succession, tu-rother sepa ation of the signal and interference vibrations may be effected.

My invent-ioncontemplates theuse of a sound reflection or refraction device where by the sonorous vibrations produced the signal" waves :afterf'separation' from the sonorousivibrations produced by the elec .trical disturbances maybe concentrated on the apparatus which reconve'rts' them into electrical vibrations. H i r.

It Will be obvious that the principle uniderlying inv nti nmay be'embodied in a great variety of apparatus and that various circuit arrangements may be employed in connection therewith for converting the energy of electromagnetic waves into SOIlOl.

ous vibrations at one end of my apparatus and for converting sonorous vibrations into readable signals at the other; and therefore it will be understood that the several embodiments of my invention hereinafter particularly described are illustrative merely and not restrictive.

In the drawings which accompany and form a part of this specification- Figure 1 is a diagram of an electromaginafter referred to in explaining the operation of my invention; 7

Fig. 8 is alongitudinal vertical section of a modification of the reflection-absorption chamber;

Fig. 9 is a longitudinal vertical section of another modification in which a reflectionabsorption chamber is interposed between the reverberation chamber andthe stationary-wave-separating chamber;

Fig. 10 is a vertical longitudinal section of a further modification in. which a reflection-absorption chamber is employed instead of the percussion and reverberation chamber;

Fig. 11 is a diagram of an electromagnetic-wave receiving-system embodying my invention wherein a counter-phase tube is employed for conveying the energy of the signal vibrations to the signal indicating device, certain parts being shown in longitudinal vertical section; i

Fig. 11 is a longitudinal vertical section of a modification of the apparatus shown in Fig. 11 wherein the ratio of the signal vibrations to the shock-excited vibrations is 2 to 1;

Fig. 12 is a longitudinal vertical section of another modification'of the system shown in Fig. 11 wherein the ratio of the signal vibrations to the shock-excited vibrations is 3 to 2; r

Fig. 13 is a longitudinal vertical section of a further modification of the system. shown in Fig. 11 wherein the percussion netic-wave chamber consists of two relatively movable tubes;

Fig. '14: is a longitudinal vertical section illustrating the application of the counterphase tube to Fig. 15 is a longitudinal vertical section showing a further modification of the apparatus represented in Fig. 14;

Fig. 16 is a vertical longitudinal section showing a further modification of the system illustrated in Fig. 11;

Fig. 17 is a diagram ofan electromagreceiving-system illustrating another modification of the system shown in Fig. 11, wherein a combined percussion and reverberation chamber is employed, certain parts being shown in vertical longitudinal section; I

Fig. 18 is a vertical longitudinal section illustrating an apparatus for accentuating the maximum concentration of the potential energy of the acoustic stationary waves in the spatializing tube;

Fig, 19 is a vertical longitudinal section illustrating a modification of the system shown in Fig. 1 wherein the shock-excited vibrations are preventedfrom forming stationary waves of sensible'amplitude in the chamber in which the acoustic signal waves are spatialized;

Fig. 20 is a vertical longitudinal section of another modification in which an open spatializing tube, excited at both ends by both sets of vibrations, is employed;

Fig. 21 is a vertical longitudinal section of a further modification in which a closed spatializingtube is excited at both ends by both sets of vibrations;

Fig. 22 is a plan view partly in section, of an apparatus embodying my invention wherein a toroidal tube is employed as an acoustic spatializer;

Fig. 23 is a vertical section taken on the line 23-23 of Fig. 22.

In the particular drawings selected for more fully disclosing the principle underlyconnected to earth at E through the inductance L shunted by the condenser C whereby the system is attuned to the'frequency of the waves the energy of which is to be received. Connected with the receiving antenna is a radio-frequency amplifier J, the in-put terminals a 6, thereof, being connected across the terminals of the inductance L or operatively associated with the antenna in any suitable manner, and the out-put terminals of said radio-frequency amplifier are connected to the in-put terminals 6, f of an audio-frequency amplifier K which includes an oscillation detector. The out-put terminals g, h of the audio-frequency amplifier are connected to an e'lectro-translating device 1 for converting the electrical vibrations developed in the receiving system by abrupt the system shown in Fig. 1;

mg my invention A represents an antenna will cause said receiver chambers 9. and 10.,

or impulsive electrical tore-es-and the elec trical vibrations developed therein by the waves the energy 'of which is to be received, as Well as the vibrations created in the-systern by interfering signal waves,into nonelectrical vibrations. v V

In the present instance the translating device 1 is shown 'as adoud speaking te'lephone receiver by which the electrical v-i-- b'rations aforesaid are converted into sonorous vibrations. 1

It willbe understood, otcoru-se that any suitable radio-frequency amplifier and ans dio-frequency amplifier may be employed for the purposes above indicated and that I do not limit myselffto the well knowvn types er such apparatus represented dia-- grammatically in Fig. 2 for completeness of disclosure.

Any suitable transmitting system can be employed in conjunction with my improvedrec'eiving system, provided that when i a tele phone receiver is employed as said translating device 1, said transmitting system to produce audible tones. Suitable transmitting systems are shown in my Lette'rs Patent Nos; 1278 507 and 1,278,508, dated September 10, 1918. Preferablya heterodyne is associated with the' receivinesystem, and in Fig. 2 I have shown in diagram andin Fig. :1 have'indicated, a heterodfrnc oscillator inductively relatedto-the inductance L by the primary I said heterodyne having the usual condenser C adjusted by the handle H andxthe adjustable condenser C The translating device 1 isoperati'wely associated with the percussion chamber2, being fitted intoan aperture in the end Wall 3 of the tube 4; in the, Lpresent instance. Sli-jdably arranged Within the tube 4 is a tube 5 having-an end wall 6, whereby the length oil the column of airbetween the end wall 6 and the partition 7 adjustably arranged Within the *tube 4 and having a central orifice 8, may be varied; v

The telescoping tuber may be of metal and the end alls 3 and 6 thereof, as Well as the partition-7, are preferably Wooden discs closely fitting the same by a lightcloth Wrap-ping such as felt. I i v The charm-be 9 between thediscs 6 and? constitutes a reverberation chamber. and-in the {present instance the Ltubular Wall oft-he percussion chamber 2 is integral with the tube 4-. although it will -be -understood, oi course. that said percussion chamber may be entirely separate from the chamber Coupling the. reverberation chamber with the stationary wavese-parating chamber 10 is a member shown-in the present instance as consisting of twotelescoping tubes 11, 12 which are preiierabrly of metal of at least one thirty second inch in thickness, and having a much smaller diameter than the opening "of said holes and 15, 16, said discs preferably being of Wood and arranged for longitudinal movement along; the tube so as to vaiy the effective tween each pair of discs. V

The stationary-Wave separatingl chamber- 10 consists of twotelescoping each preferably oi metal and having end Walls 23, 24, respectively,which are preferably wooden discs.

Midway between the chamber 10 there. be placed"a partition tubes 21, 22. 1

end Walls or are the distance bei 25 preferably of Wood and provided with a 7 number of apertures 26 fi'lled With tufls of hair, felt or other sou nd'fabsorbing porous material 27. i i

Couplin the stationary-wsiveseparating chamber with the reflection' absorption chamber 28 pairzof telescoping tubes 29 30 similar inall respects to the tubes 11,

12; respectively, said tubes beingprovided with a series of radial aperturesj31', 32 and pick-up discs'33, 341- and 35, 36.

The reflection-absorption chamber 28 consists of "two sections preferably of Wood, the,

inner surfacesof which are ellipsoids or paraboloids of revolution, Which may be slightly separated and a sheet of felt 87 or thelike, or a diaphragm similar to the diaphragm 25, placed therebetvveen."' Each section of the chamber 28 is provided With a plug 38,39, ad ustable longitudinally of the major axis-of saidchamber.the j'uxtaposedsurfaces of NlTIQll preferably are iden-' tical With those of the sections of the chamber in Which'they are placed" Suspended, from the top all of the chamber 28 in any-suitable 1nanneris a translating .device capable of converting sound Waves into electrical vibrations, such' device being placed with its driven member In the'present at ailiOCl-IS of said chamber instance the translating: ice is shorvnas an electromagnetic telephone' transmitter 4:0 suspended by Wires j'rssing through the plug 41 which fits into aperture in the tOp fif theacha mber. 1 a

The transmitter 4015 connected to-the i-nput terminals m n ofthe audio-irequency amplifier M-, an'd, the out-put -te rminals 01-7), thereof are connected to indicating);

device T, across the terminals of which may be connected an audibility meter N.-

It will be *understood of coursnthattho detailsgof the audi-freq fiency ampliiier M a l which 1 have shown in; Fig... 3 are for pur-- poses of illustration only, and-that I do not limit myself to the use thereof.

The foregoing is a brief description of one of the precise arrangements of apparatus and circuits wherein I haveeembodi'ed my invention in practice. A detailed description of the same giving the sizes and proportions of parts which were found to give good results, as well as the modeof operation thereof, and the theory underlying the same, will now be set forth.

The arrangement of apparatus and cir cuits shown in Fig. 1 constitutes a complete acoustic filter consisting of seven elements starting with the generator ofacoustic vibrations and ending with the signal indicating device for using the acoustic vibrations making up the signal to be received when filtered clear of undesired acoustic vibrations created by electrical-disturbances or by interfering signals, as follows:

I, the electromagnetic-wave receiving-system comprising the loud-speaking telephone 1 or other generator of acoustic vibrations;

' II, the filter-coupling device or percussion chamber 2; III, the reverberating device or I echo chamber 9; IV, the resonant filtercoupling device 11, 12; V, the stationary wave separting-device or stationary-wave chamber 10; VI, the filter-coupling device comprising the tubes 29, 80 and the reflection-absorption chamber 28; VII, the indicating or recording apparatus comprising the translating device 40, the reamplifier M,

' if employed, and thesignal indicating ,de-

vice T.

As" above stated sist of any suitableelectromagnetic-wave'receiving-system' provided with a loud-speaking telephone such for example, as the magnavox' reproduc'er, which I have found to be well suited for purpose. 7

The element II or"perc ussion chamber. consists of asound chamber in the form of a cylinder the length of which is small compared to the wave length of the acoustic vibrations passing through the apparatus. The velocity of sound in air being about 13,500" per second, it follows that a sound wave having a frequency of 1000 cycles per second will be 13.5 long and therefore when the apparatus is designed so that abrupt or impulsive electrical forces will produce acoustic vibrations of said frequency in the reverberation chamber, the distance between the two walls 3, 7, of the percussion chamber should be small compared to 13.5". In general, it should never be longer than a quarter wave length of the" vibrations having the lowest frequency which pass through the system. 7 e

The element III or reverberating device consisting as aforesaid of thetelescoping tubes 4, 5 is about three inches in internal diameter and hasja hole not'smaller than the element I may elm three-eighths inch in the center ofits end wall 6, the hole 8 similarly located in the end wall 7 having approximately the same di-: The telescoping tubes. 4:, 5 are mension. from seven inches to ten inches in length,

the tube A} which forms part of thepercusa which preferably are in the ratio of l to 2' or 2 t0 3. j i Y The general rule which I have followed in the use of this apparatus is as follows ('1) Choose an audio-frequency which is coincident with some interfering beat-toneor spark-tone produced by the loud-speaking telephone, this being the frequency of the vibrations to be eliminated.

tube 5 with-respect to the tube 1, to the said audio-frequency. (.3) Select a frequency for passage through the complete apparatus whose half wave-length is an integral submultiple of a half wave length of the fre quency t0 be eliminated, for'example. if the" frequency to be 'eliminatedis 500, the frequency to be transmitted through the'apparatus may be 1000, 2000, 3000 cycles, et-c.-'

Tune the'reverberating chamber 9, by sliding the When the reverberating device 9 IS a cylinder, it will pass all such frequencies when it is attuned so thatits fundamental is equal to 500 cycles.

1 When abrupt or lmpulsive electrical forces cause the loud-speaking telephone 1 to produce a non-impulsive acoustic disturbance muchlofithe energy ofthe resulting complex vibration will be dissipated in the per-- cussion chamber 2, and the energy remaining therein will effect the shock-excitation of the air in the reverberating chamber 9.

which will vibrate at its fundamental and all the harmonics thereof. Inasmuch as by far the larger part of the energy of said vibrations so created in the reverberation chamher is contained in the fundamental vibration' thereof, the harmonics of said fundamental may be neglected. for whatever energy is embodied in said harmonics excited by acoustically shocking the reverberation chamber may be filtered out by the filter couplings IV and VI, any-unconverted energy from said impulses beingheard at the out-put end masked by the signal, since they will be of such'small' amplitude that the signal-interference ratio is very high.

It is'of course essentialthat the frequency of the shock-excited vibrations be different from that of the useful or signal vibrations. and the latter may be selected to correspond to an upper harmonic of the reverberation chamber 9 1n the arrangement shown in Fig.

1, or as explained in connection with Fig.

11, they ma correspond to the fundamental of said reverberation'chamber. In any event the frequency of the signal vibrations, in'the case of the apparatus shown in Fig. 1, ought to be sufficiently different from the fundamental and upper harmonics "of the reverberat-ioi'i chamber to ensure against the excitation thereof, in an'appreciable degree in said chamber, by acoustic shocks.

Referring to Fig. 4, the reverberation cl-iaiinbei' is about 6.75 long and its funda mental therefore is 1000 cycles. The curve Kn is that of the spatialized acoustic motion constituting the kinetic energy of a stationary wave developed in the reverberation chamber *9 by a non-harmonic acoustic disturbance produced in the percussion cham her 2 by the loudspeaking telephone receiver 1, as for example, by interrupting a circuit including said receiver and abattery about twelve times per second, and the curve Pal/ represents the space pressure variation of the potential energy ofsaid wave. Obviously the irregular non-harmonic disturbances produced by the receiver 1 when the receiving antenna is acted uponby abrupt or impulsive electrical forces will be converted into spatialiyed periodic vibrations having, in the present instance, a frequency of 1000 cycles per second, and the motion and pressure curves thereof will have approximately the form shown by the curves Kn, Pa, aforesaid. I

The pitch of the acoustic signal vibrations produced by said receiver 1 when the antenna A is acted upon by electromagnetic signal waves is under the control of the operator, who, by adjusting the heterodyne 'I-I, may, in the present instance, make said pitch equal to 2000 vibrations per second. In Fig. 4 the curves Kn and Pa represent the spatialized motion and pressure curves of said acoustic signal vibrations, and, as the two sets of acoustic waves are of difierent frequencies, they are, of course, cyclically dephased along the axis of the reverberation chamber.

Any suitable apparatus may be employed in connection with the reverberation chamher to pick up the sound wave produced by the signal vibrations at a point where the amplitude thereof is large compared to that of the sound have produced by the electrical disturbance. For instance, the pick-up tube 12 may be so positioned with respect to the reverberation chamber that its openings 15 are at a pressure loopor the maximum ordinate of ,the curve Pa and at a pressure node of the curve Pu so that the sound. heard at the outer end of said tube will consist in large part of the tone produced by the signal vibrations, the energy of the stationary wave PM formed by the disturbances being substantially masked by the signal tone. Therefore, if desired, a translating an e vibrations by transmission through severa-l stationary-wave separating devices in succession, and to 'reoonvert the'acousti'cs nal vibrations into electrical vibrations which are used to actuate the signalindi eatin device; i

In Fig. '5 where the length of thecha'mber -9"is shown as 13:5" the fundamental of the reverberation chamber is 500 a ndcor= responds tea half wave length of 1-8.5; In this case the signal tone may have a f r q-uency of 15 00 as ind-i'catedby the curves Pm and Kn. a a I,

The tube 12 is placed so thatitsepenings 15 are at a maximum of the curve atwhi'ch point the ordinate of the curve Pa, while not zero, is considerably; less than that of the curve In such case, 'thej si-gnal interference ratio may be made as high as desired by successive transmissions of the two sets of waves through stationary-wave separatingdevices.

InFig. 6 the fundamentalof the rever l e-ration chamber is taken as before as500', and the frequency of the signal vibrations is selected as the octave thereof. The openings 15 of the tube' 12,'may, in this instance, be located at a pressure loop of :the signal-Vt brations and a pressure node of the vibrations created by the disturbances.

It will be understood of course that the values and dimensions given above are merely examples of various ways in which my apparatus maybe constructed and used.

The element IV or resonant filter coupling consisting of the two telescoping tubes 11, 12 which may be from one quarter inch to one half inch internal diameter, approximately, is attuned to offer no impedance to the passage of sound waves having the pitch of the signal vibrations and to oppose the passage of sound waves of other frequencies, such as the sound waves created in the reverberation chamber by the electrical disturb ances. The. openings 15, 16 near the ends of the tubes are, in the present instance, not less than one-eighth inch, nor more than one quarter inch, in diameter andv preferably four such openings areiplaced at-a dis tance from the end, 0f,,each tube less than the diameter thereof. The diameter of] the pick-up discs 17, 18 and 19,20, as well as those placed at "or near the ends of the tubes 29, 30, preferably are approximately fifty five per ce'ntof the diameter of the reverberation chamber 9 of the stationary wave separating chamber 10. The separa tion of-eachpairof-discs may vary from one quarter to the;;to,ta-l diameter oftthe holes 15., 1'6, 81, .32. The closer this separation the sharper the power of theacoustic filter coupling to discriminate between the desired and undesired stationary waves. The smallest advisable separation is one-sixteenth inch. The openings 15, 16 act as acoustic couplings between the vibrations set up in the air column in the reverberation chamber 9 and those set up in the air column of the stationary-wave separating chamber 10. When the opening 15 is at a cross section of the chamber 9 where there is little motion of the air particles and large pressure variation, it. transmits .such pressure through the tubes 11, 12. This would occur, as shown in Fig. 4, at or near the ends of the chamber 9 under all conditions and at adistance from either end. equal to an in tegral multiple of a half wave lengthof any acoustic stationary wave formed therein by the periodic vibrations to be received.

. In the present instance the. filter coupling 11, 12 is attuned to 2000 cycles and therefore its length is approximately 13.5 between the planes passing through the cen ters of the two series of holes 15. 16.

It will be evident that the shorter the half wave length between the points 9, 1 in Fig. 4 where the pressure stationary-wave curve Pa crosses the zero axis,- the smaller will be the displacement of the pick-up holes 15 from the maximum ordinate of said curve, where maximum action in the tubes 11, 12 is obtained, to the said points 9, r, where minimum action is produced,in other words, the stationary-wave tuning is sharper in terms of bodily displacement of the coupling device ll, 12 along the axis of the reverberation chamber. It is also made sharper by reducing the separation of the pick-up discs 17, 18 at the expense of the energy ransmitted into the filter coupling. By virtue of this fact, broad tuning by the pickup discs is made possible as will hereinafter be explained when forced acoustic vibrations which are not constant in frequency are developed in the reverberation chamber.

A resonant filter-coupling devicesuch as the tubes 11, 12 isnot absolutely essential, but I prefer to use the same in order to,

5 transmit the largest possible amount of the energy of the vibrations of the desired frequency to the succeeding element of the system, the stationary-wave separating device 10.

The element V or the stationary-wave separating-chamber has substantially the same construction as the echo chamber 9, and must be as long at least as a half wave length in air of the vibrations of the lowest frequency used. Itslength is adjusted as hereinafter more fully set forth until a maximum of sound for both the desired and undesired frequencies is detected at the opening through which the tube 30 passes, by a Stethoscope or other listening device.

Hence the stationary-wave separatingdevice will resonate to vibrations of several frequencies simultaneously present therein, as shown in Fig. 5 where the curve Pa represents the space-pressure variation of a I sound wave whose half wave length is 13.5

and whose frequency therefore is 500, which isthe fundamental of said device, the curve Pn represents the space-pressure variation of-a vibration having a half wave length of 6.75 and whose frequency therefore is 1000, which is the octave or first even harmonic of said device, and the curve Pn represents the space-pressure variation of a vibration having a half wave length of 4.5 and whose frequency is therefore 1500 this-being the first odd harmonic of said device.

Inspection of Fig. 5 will show that at or near the end wall 24 of the wave-separating chamber 10, there will be a maximum of air pressure for every frequency to which the chamber is resonant, and also that at cross sections of said chamber which are distant one third, one'half or two thirds of the length of said chamber from either end thereof, there is a region where any detecting apparatus sensitive to air vibrations will give a maximum response for the above mentioned frequencies, respectively.

Preferably a. partition is placed at a point midway between the ends of the chamber 10 for the purpose of reducing the amplitude of the fundamental vibration developed therein by the electrical disturbances which are to be eliminated. One of the various forms of partition which may be used for this purpose is shown at 25 in Fig. 1 and consists of a disc of wood about one quarter inch thick provided with a plurality of holes 26 each having a diameter equal approximately'to five per cent of the diameter of the partition and the combined area of which is equal to about fifty per cent of the area of said partition, said holes being filled with porous sound-absorbing material. It will be obvious that various other forms of partition such for example as that shown at 37, viz, a sheet of felt or the like, may be employed in the chamber 10.

Referring to Fig. 5, for example, it will be noted that the curve Pn crosses the zero axis at a point midway between the ends of the tube,-in' other words that the fundamental has a pressure node at this point,-- and that the octave represented by the curve Pn has a pressure loop at the samepoint. If'the formation of a node of pressure in the fundamental is prevented by a partition, such as above described, the fundamental will be broken up'and practically suppressed because at the point where such'fundamental has a node of pressure, it has also a loop of motion as shown by the curve Kn, and such motion is destroyed by the presence of said perforated diaphragm. No appreciable effect, however, is noticed on the stationary pressure wave Pit of the octave, because the diaphragm 25 has very small effect where there is very little acoustic motion among the air particles, but considerable pressure variation, there being a motion node (not shown) for the octave at the point where such octave has a pressure loop. In other words, the energy of the octave at this point being practically all potential instead of kinetic, vibrati-onshaving a frequency of 1000 will pass the diaphragm while those having a frequency of 500, the energy of which at this point is practically all kinetic, will be practically suppressed.

It will be understood of course that the employment of the said partition is optional. Under certain conditions its use is desirable to help break up the clang which is an effect caused by the tendency of sound to persist on account of continued vibration of the air in the various chambers of my apparatus after the incoming signal has ceased to excite the acoustic system. This persistence of vibration under certain circi'i-mstances causes the dots and dashes of the telegraphic code to run together so that signals are sometimes diflicult to read. This may be diminishedby using higher frequencies for the signal tone and by the employment of the diaphragm aforesaid, and by diminishing the volume of air used.

The element VI or the filter coupling device comprising the tubes 29, 30 and the reflection-absorption chamber 28 is 'em pl'oyed for still further filtering out the spatia'lized acoustic vibrations produced by the electrical disturbances. The tubes 29', 30 are substantially the same in construction as the resonant filter-coupling device IV, except that in the present instance the end plug 42 and the pick-up discs 33, 34 may, if desired, be eliminated. The dimen sions of the reflection-absorption chamber are such that its major axis is equal approximately to a full wave length of the signal frequency. The opening 31 of the tube 29 is kept at one of the foci of the chamber-28,

and the electromagnetic telephone transmit ter 40, or other converting device, is maintained so that its diaphragm or driven memher is at the other focus. The two halvesof the chamber need not be in contact, but may be separatedby about one-half inch and in such case itis optional to place a diaphragm of sound absorbing materialfsuich as the felt disc 37 or the perforated wooden disc nals. The signal indicating phone transmitter with a battery in its circuit, may be employed.

(2) It establishes a stationary acoustic wave whose pressure loops are made to have a greater degree of sharpness in their effect on the converting device 40 when the acoustic frequency varies, than they exhibit in either the stationary-wave-separating chamber 10 v plug 39 is used to tune the filter coupling device, VI, by slight longitudinal movement along the major axis of the chamber 28. Usually it will suppress a high pitch signal if moved along said axis not more than one-eighth inch, and a frequency variation of 2.5% harmonic vibration in the converting device 40 to disappear.

The position of the hole which accommodates the plug 41, above described, is best located firstby calculation and then checked empirically, and is arranged so that the di aphragin or driven member of the converter 40 will be approximately at one of the foci of the chamber. r

The element VII comprising the converting device 40 and the apparatus associated therewith may consist of any suitable system of circuits and electrical instruments for -converting the electrical vibrations developed by the transmitter 40 into readable sigdevice may be a head telephone or, where the audibility of the received signal or soundsis suiiicientlygreat and a record thereof is desired, it may be a 'd'i'ctaphon'eor similar apparatus. Obviously the re-amplifier shown in detail in Figure 3, need not beused. I prefer to will be sufficient to cause the i other or the echo chamber 9. The

secure an amplification of aud ibility in the re-amplifier of at least 2000 times in order to obtain satisfactory operation if the sig nal tones produced by the loud-speaking telephone 1 has a strength denoted by at'least 500 audibility. It will be understood of course that the audibility meter N while con venient, is not essential for the accomplish ment of the result sought by the present invention. v Y

The operation of the system shown in Figlwisasfollows: I r

The percussion and reverberation chamhere are adjusted by relative longitudinal movement of the tubes 1 and 5 and the partition 7 so that an interruption of the current in the transmitter 1 will produce in the reverberation chamber a vibration having the same frequency as the most pronounced interfering audio-frequency of a wireless telegraph transmitting station. The adjustment of said chambers may conveniently be tested among other ways by in serting a flexible ear tube intothe reverberation chamber through the opening by which the tube 12 passes into the same. It is to be noted that the length of the air column in the reverberation chamber which would be indicated by theory as the half wave length of a vibration of given frequency is slightly modified by the presence of the percussion chamber so that, for example such air column would not be precisely 6.75 when said chamber is to resonate to a frequency of 2000 or to develop vibrations of a frequency of 1.000 when shock-excited. After the filter-coupling 11 and 12 and the stationarywave-separating chamber 10 are added, the reverberation chamber must be slightly readjusted because of the effect of the added apparatus on the fundamental thereof.

The filter-coupling device 11, 12 is tuned to the fundamental of the reverberation chamber, that is, to the frequency of the vibrations excited in the latter by acoustic shocks, which frequency, as above stated, may be taken as the audio-frequency of the most pronounced interfering signal. The filter-coupling device 11, 12 may conveniently be tuned to the fundamental of the reverberation chamber by listening at the opening 16 of said coupling with an ear tube.

The stationary-wave separating-chamber 10 is now added and adjusted until an ear tube, stethoscope or other suitable device placed at the opening through which the tube 30 enters said chamber, shows that the whole system from the transmitter 1, to and including the stationary-wave separating chamber, is in resonance to the shock tone originally excited in the reverberation chamher, said shook-tone being, of course, the fundamental of said chamber as modified by the associated apparatus, that is to say, the frequency at which said chamber vibrates periodically when abrupt or impulsive electrical forces such as static disturbances act upon the antenna.

By adjustment of the micrometer condenser C'", the tone of the signals to be received by the system is varied until a resonant condition in the chamber 10 is indicated by the same ear tube or other listening apparatus which was used to check the shock-wave resonance therein.

The resonant filter-coupling 11, 12 is again adjusted to give the best resonant value in the chamber 10 for both the shock and signal waves.

The filter-coupling V1 is then added and tuned to resonance with the signal tone, using the pick-up discs 33, 34, located as aforesaid at one of the focal points of the reflection-absorption chamber, and having the converting device 40 at the other focal point thereof, although, if desired, a plain open-ended tube may be used in place of the tube 29 the end of which is provided with said pick-up discs 33, 34. The final adjustment of the chamber 28 consists of a slight longitudinal movement of the plug 38 so that the desired signal is heard at a maximum in the signal-indicating device T' which may be a head telephone, whereupon the plug 39 is also moved slightly longitudinally until another maximum is heard in the telephone T. j i

A final observation is made on static audibility, that is to say, the audibility of the vibrations produced when the circuit of the receiver 1 is suddenly interrupted and the reverberation chamber thereby shock-excited, by using the audibility meter N and retuning the percussion and stationary-wave separating chambers successively to get the least possible audibility in said meter of the static or shock-excited tone heard in the telephone T. I

A signal of less than unit audibility, if measured at the in-put side of the radiofrequency amplifier J, is amplified by-the latter to one having an audibility of 300 at least and this again is amplified by the audio-frequency amplifier to a signal having an audibility of more than 3000.

The static disturbances set up in the tuned antenna system by atmospheric electrical charges cause additional sounds in the loudspeaking telephone 1 of an average intensity several times as great as the signals.

These static disturbances, although generally greater in intensity than the signals, can be ignored by a skilled operator if they are not greater than four times the signal strength. They are amplified together with the signal and at the loud-speaking transmitter 1, their ratio to the signal is practically the same as at the in-put terminals of the radio-frequency amplifier J, the audibility of said electrical shocks at the receiver 1 ranging from 3000 to 30,000 as determined by the auxiliary telephone T or an audibility meter. Under such circumstances it is impossible to read the signals produced by the receiver 1 as they are completely masked by the irregular non-harmonic acoustic disturbances static disturbances.

The percussion chamber 9 takes up a large part of the acoustic shock from the receiver 1 and determines the shape of the initial produced by the inserting a stethoscope at ariouspoijnts' therein, it is founclthat itdiminishes together with the signal; audibility until, at the intake of the chamber 10:, --the signal ,vibr'ations and t l-rose produced- -byrthe; s'tat'ic-gd-isturhances have about-one halt the a-tidibility which: they had at theontlet 8 ef the per- CUSSlOn chamber or the in' takepof theecho chamber; At the" iii-take 32 0f therfilten coupling device VI,- the ratio o'fsignahtb static is reversed so that the sign'alwis-at least ten times-the statioaudihility." -Mo reover; the "au'dihility :cf the=-various frequencies p resent throughdut 'the apparatus, which are due to inter fering andimfieqiiency signals or heterodyne beati-freqiienci'es are reduced to avalue not greater-than a' 'fi action off the strength of --tlie desired signaIwhen observed at'the focal po'int -31 of the l refleciiomabsorption chamberl.

, The-fabric partition 37 reduces the static "andibilityto-less than ten per cent andin some cases to less thancne per cent ofthe signal; when the 'acoustic' signal 'Wavei's the octave of the acoustic static Wave; that is, whenthe audio-frequency of the si'gn'a'l to be of the interfering si gn als, that? is, the signals from other stations hav'ing audiofrequenreceived, to less than twenty lper' cent of the a-udihility' ofthe"desired signals, andfty making the re z'tnip lifiei M resonant' to the audio-frequenoy of the' sign'als to "be received, such interfering signals may be i'edn'ced to less 'than five per "cent ct theaudihility of the signals to be re'ce'i'x' ed, v

Thus it will he see'nthat; by aae'ansof'th'e apparatus above de'scrih'edl"I ai n' ah'le to ch a n gewaeigaal static ratim'of '1 toll); to late 51 aud ts-receive signals which other wise would lie/completely maske'tlhy static, and I hate reduced the =audibi'l'ity'ot static disturbances"from more tli an 3000 to an ave-rage of 50, the range of reduction being between 11 and-300 whileat the-same time reducing theclang-. r a

It will benoted' that evenalthough' 'the receiving sys'teln is "not acted upion by abrupt or impulsive "electrical forces, "any apparaths'hfi'orcls a 'nieans' for selecting the desired signal from those transmittedby other stations and that this may be accom- =plished hy attunin-g' thereverberation-chainfslponds; to I an Wave length of the inte1'fering7--sign"al,-

tound here the statijo th erei'nfby said inte hays a r llllllllll ll-lll efieot on thetubef30and V iy-here fthe desired way' es ,l i-aye 5a maximum i ui-idiesired' Waves isa maximum.

her to the audio-trequency of interfering signal, modifying the audio-frequency of thesignal to be receivedfso that it co'rreneafie i U' -mlflf ili a h spatifa li-zing the two sets o'fstationary, Waves -thereb-y' setup andpicking up the ene gy jof the desired signal Waves at a point Where the amplitude of the same is large compared with the amplitude of the interferingw'ayest Whether thejapparatus' is employed to eliminate the efi'ect on the signal indicating device of 'vibrations'created in the system by abrupt or; impulsive electrical forces or vibrations created therein by interfering sign al waves, the I construction a and mode of opera-- txon of said apparatus s thesa me-s y WY-he-re nu-m'h'er of interfer ng signal fivayes having fdifierent audioflfequejncies impinge upon the antnnay sonie point the r stationary-Waye sep'arating-deyice may be e r -l Wa es, s t '1 P 11 s cee waves 41 eliect thereon, or at least Wherethe ratielojt the desired wave --t 0 the l'esul tantfof the This pos sible because of rthe adjustable :lpo sit'ion of the pick-up. discs each pair "of Which, in I s c ca e ll be m re W de y ep ated than when emlployed-to discriminate loetween the stationary-faves "produced static disturbances and those produced by the desired signals. l I

I have already a dverted to thefact that broad tuning; is n ade possible by the aforesaid longitudinal adj usta uqa discs and that this feature is important when the frequency of th i not; constant. It will be I oby ious that a slight change in the frequency of the transmitti'ng generator and therefore r the an Clio-frequency o f the signal to be ieceiyed will shift the maxima of .the stationa r Wave-s produced in thecha-inber 10 "so that under certain conditions a maximum of such signal. Wave Will beshi-fted beyond the openinghetween the piclz up discs 35,

ing. Thisdifiiculty can usuallybe reincdied, if the changeinthe frequency of the transmitted wavesis not too great, byincreasing the separation of said pick-up discs.

Inasmuch as the acoustic systemis very sensitive to noises created inits proximity,

z y l fl'l Pi 7 e Waves is I 1 '36 if the separation of the jlatterfwas'; ]1nade sma-llto increasethe Sh-MIJHQSSQf the tun and connecting elements need not have the shapes hereinbefore described.

Referring again to Figs. 4 to 7 on which, without intent to limit my invention thereto, I have placed dimensions and frequency values, it will be apparent that the periodic vibration of frequency it created in the echo chamber 9 will be transmitted by the coupling-device 11, 12 to the stationary-wave separating-chamber 10, the space-motion curve of such vibration being shown at Kn' and the corresponding space-pressure curve thereof at Pa. In like manner the stationary-wave of frequency n created in theyecho chamber by the desired signal will produce in the chamber 10 a stationary sound wave of which Kn is the motion, curve. and P'n is the pressure curve. 'In Fig. 4 the opening 32 of the tube 80 is placed at a zero point of the curveP'n' which is a maximum point of the curve Pn, so that the amplitude in saidtube of the vibrations resulting from the signal waves is large compared to the amplitude therein of the vibrations resulting from the abrupt or impulsive electrical impulses.

In Fig. 5 the tube 30 is so located that the opening'32- is at a cross section of the chamber 10 where the ordinate'of the pressure curve P n is larger than that of the curve Pn so that, although thelatter is notzero, a much greater effect is produced -in the coupling-device VI by the desired waves than bythose resulting from the electrical disturbances.

In Fig. 6 the opening 32 of'the tube 30 is placed at a point where the stationary wave produced by the static disturbances has a pressure node and that created by the signal vibrations has a pressure loop, this also being the case illustrated in'Fig. 7

It is to be understood'that the diagrams shown in Figs. 4 to 7, inclusive, are merely illustrative and that various other ratios of signal frequency to static frequency which may be employed will readily occur to those skilled in the art.

It is also apparent that while 'I have shown in Fig. 4 a stationary-wave separating-chamber whose first even harmonic is equal to the fundamental of'the reverberation chamber and in Figs. 5, 6 and 7,-stationary-wave separating chambers whose fundamentals are equal respectively to those of their associated reverberationchambers, various other proportions may be adopted without departingfrom the principle upon which my invention is founded.

In Fig. 8 the converting device 40 is secured to the end of a tube i passing through a hole in the axis of the tuning through a hole in said tube and are connected as in Flg. 1 to the m-put terminals ofthe-audio frequency amplifier M. It'is desirable to separate the two halves of the reflection-absorption chamber when even harmonics :of the fundamental frequency of said chamber are prominent therein. As indicated the tube 29', passing through the plug38, may be open-ended, and the pickup discs omitted. y

In Fig-9 I have shown a modification wherin the reflection-absorption chamber is inserted between the echo chamber 9 and the stationary-wave-separating chamber 10 to still furtherweaken thevibrations produced'by electrical disturbances. In this case, the telescopingtubes 11, 12 connect the chamber Q'Wli'l'l the chamber 2S and the two telescoping tubes 11",12, connect the lattenwith the chamber 10. In this in- "stance the tube lwhich forms part of the percussion chamber is separate from the tube 1 of the reverberation chamber and is shown as extend ng half way over the partition .7 which'separates said chambers. The fact-that the percussion chamber 2:

is substantially at filter-coupling is shown clearly in Fig. 10 wherein the percussion chamber is replacedby the reflection-obsorption chamber 28 illustrated as consisting of two sections, the inner surface of each of which is a paraboloid of revolution, and by the adjustable resonator 11", 12' having sound-proof connections between the transmitter 1 and the chamber 28. In this case the tuning plugs 38, .39. are each given a paraboloid surface corresponding to that of the sections in which they are located. This permits of greater longitudinal separation if desiredbetwe'en the two sections making up the chamber-than is generally possible with an ellipsoidal type of chamber such as shown in Figs. 1, 8 and 9. The adjust able resonator 11, 12 has sound-proof connections between the chamber 28 and the reverberation chamber 9.

It will be understood without further explanation that the adjustment and mode of operation of the modification shown in Figs. 8,9 and 10 are the same as above set forth in connection with Fig. 1.

The embodiment of my invention above described is preferred by me for efiiciency, but I prefer the embodimentthereof shown in Fig. 11 forsimplicity.

In Fig. 11 I have eliminated the reverberation chamber and the reflection-absorpreceiving-system including the loudspeaking telephone receiver 1, such as already 'described in connection with Fig. 1.. plug 39, and the leads of said device pass The element II is a percussion chamber quarter; to I one.- half' of the wave length. of

percussion chamber; IIethan in the caseof the percussion chamber IL: oil-Fig. 1; In some casesil have; made; the-length of; said percussion chamber; TIE about tines-.eighthsi of a. complete wave length. of; the; acoustic signal waves, but this length 1 depends-some.- what tlPOlLtllQ-Jltltlllfl otthe joint between the tra nemitter 1 and tube iii, and,;ii-, such j oint is not; airtight upon .the, separation o t. these lem n s. I t

A ter alt her adjustments have en. madel PIGfQIytO test; the; adjustmen t of. the length of; the percussion chamber by. vary ing the separation tl' ereof; witlrrespect. to. he ransmitter nt l e; hes s ml= at ratio-is notedin the signa-liin dicating; 5 device. T. The inbernalj diameter of; the tube. ifnis about one. third otgits en'tern-al; diameter, and it is placed against a woodendisc 23'; which close y: fl t-S. the, .tubetfi, and closes one end 10f the statiQnaly-wave+separa-tinge chan l: bet-'10 the other .end of which 1 isclosed by the disc 24. closelyz fitting the,tubeadwhich has telescopic connection, with said-tube-47. As, shown the percussion; chamber tube 45 is; inserted intothe tube 47,. and the discs 23,, 24. may be-adjusted,longitudinally oi: the tubes .in -which they. are I placed.

. It will be obvious however, that a. single tube having. adjustable closure discs, may be used. in placecot the. telescoping tubes a7, 4.8. r J

The closure disc 23"i s provided with. a central opening 49 having a: diameter p re-t erahly smaller than2 that; of the internal diameterof the tube-4m Inonesehof. ap parat us, which I. have. used, the. length of the tube. 4-5 .Was 7 4.57. its internal, diameter 1 and its external: diameteri its .sep aration from the transmitter l. .was-..2 5-, the width of thedisc 23'. was; .5, itsidiameter was 3." and; the central opening; eat-hereof was .375. p V,

The element V. is a, stationary-Wave separating device formed in i the i present in; stance by the telescoping tubes.4L2, 41-8 and their slidableend closures Pryadjusting the position of the closure disc Qet or by changing; the, relative; position of; oneofthe tubes with respect to, i the others, longitudie n ally, the ,stationary wavewseparating -cham her 10- may. be made to resonate to the acoustic signal; Waves which; make up; the sinna-lsto be received; aIrdutO-theperiodic vibrations developed by; the receiver '1 in ing s pacepressure ourve being shown at Pvt... The curve Kn represents the space-motion.

curve of the acoustic waves developedin the chamber 10" by abrupt or. impulsive 618C. trical forcesor static disturbances, andathei cunve PW?- is the. corresponding space-pres sure curve; In the presentinstance the; length of the chamber 10 is.13.5; approx i mately. The fundamental thereof is 500 cyclesper; second; which is the frequency. or pitch. selected; for the. acoustic signal waves an d: the frequency or pitch of: the. stationary wave developed therein thy. static disturbances; is 1000 cycles. per,- second or the first even harmonic or the octave; thereof;

Itwill :1 be noted" that this is just the reverse of i the practice discussedsabove in connection with the embodiment ofs'my inuent-ionshown in Fig. 1, where thempitch oftl1e;..acoustic signal waves was: chosen as; a. multiple: of the periodic vibrations creatediimtli'e lBVGle be-ration chamber. by static; disturbances, which has the advantageithati lt'xlS generally easier to embody static: on shock-excited acoustic waves at the, "fundamental.frequency of the stationalyavave chamber! than at; the octave or other.harmonics,thereof. V

However, as. indicateddiagrammatically in Fig; 11*, it' is. preferable, generally, to select, the. fundamental 1 of the chamber: 10" as the-frequency. of the waves excited there;- in by the static disturbancesaud to useithe octave thereof as the acoustic signalwave frequency. In the case where; the: cham= her. 10 is..13...5," in length, thesfrequcncy-n of the.shock-excited.wavestwillbe 500*tl1ld1 thatvof the acoustic signal-waves:-100,a the curve. Kn representingv the space-motion curve o tthe standing; aco stic waves formed in, said chamber 10 by electricah disturb: ances, the curve PM, the. corresponding spacewpressure curve, and the curvesaKn-and Rn,representingthe space-motion;and; space.- pressure curves, respectively, oftheistandingt acoustic signal Wave formed? in 1 saidcham-. ber. V i a As. more fully explained. in connection with Fig; 12-, the ratioofthe=desiredtovthe undesiredf acoustic vibrations may. be:- 3 .to 2; in. which case thefrequency nrof the shock-excited or. undesired waves, repre sented the curves :Kn" and P71. may be 1000,and thahof thedesired .or signal waves, represented. by. thecurves Kn, Pu, may be 1500.

It will fbe: obvious that by. proper. adjustment ofithe apparatus, various other; ratios 

